1. Field of the Invention
This invention relates to surface treatments for textiles and paper products for imparting resistance to impregnation by liquid to the treated materials, and in particular is directed to gas plasma treatments for that purpose.
2. State of the Prior Art
The production of high quality textiles or paper calls for efficient methods for imparting soil-resistance to the textile or paper materials. Polymer surface coatings have been used to this end. Currently practiced methods of coating a paper surface with such a film involve at least seven distinct stages:
synthesis of a monomer; PA1 polymerization of the monomer with formation of intermediate or end polymer; PA1 preparation of a film forming solution; PA1 cleaning of the surface or application of a bonding agent to the surface; PA1 application of the coating; PA1 drying of the coating; PA1 solidification of the coating.
The basic disadvantages of these methods include the large number of stages involved in the process as well as unevenness and excessive thickness of the resultant coating, which leads to a change in the appearance of the treated material.
Japanese patent 63-75002 describes treatment in an impulse or pulsed discharge in an atmosphere comprising the gases CH.sub.4, C.sub.2 H.sub.6 or C.sub.4 H.sub.10 for increasing the durability and thermal stability of ferromagnetic layers of magnetic tapes. This method cannot be applied to fabrics because the film formed during the process changes the appearance of the treated surface.
Another prior method of achieving film plasma polymerization, described in U.S. Pat. No. 4,188,426, includes treatment in a glow discharge of per-fluoro-cyclo-butane or hexafluoroethane to reduce the friction coefficient and to improve the surface hydrophobia of organic and inorganic substrates (e.g. polyethylene films, metals). This method also cannot be applied to fabrics because the film formed during the process changes the appearance of the treated surface. In addition, the use of fluoro containing monomers is contraindicated by ecological considerations.
A known method of water and oil repellent finishing of textiles, described in USSR Patent 1,158,634, includes plasma treatment in a glow discharge in an atmosphere of inorganic gases, followed by treatment with a fluoro containing acrylic monomer in gas phase. The first stage of the process can cause additional destruction of archival documents when the documents interact with the gas that creates the plasma. The second stage forms too rough a film.
Another prior method of plasma formation of a thin film on the surface of polymer material, described in Japanese Patent 62-132940, includes:
1. plasma treatment in a glow discharge in an atmosphere of H.sub.2,CO,N.sub.2,O.sub.2 gases;
2. plasma polymerization; and
3. treatment in hydrogen plasma.
The first stage is used to improve adhesion of the film surface for the subsequent polymerization stage. This first stage lasts from 20 sec to 30 minutes of time and can cause additional destruction of archive documents when the documents interact with the gas that creates the plasma.
A prior method described in USSR patent 642550 for treatment of rubber articles includes, treatment in a glow discharge; immersion in an emulsion of polytetra-fluoro-ethylene; and treatment by glow discharge. The application of fluoro-containing monomers is an ecologically detrimental feature of this method.
Japan patent 62-260836 describes a surface plasma polymerization treatment of glass or synthetic sponges, including treatment in a glow discharge in an atmosphere of nitroethane or nitropropane. This method cannot be applied fabrics or paper because the film formed by the process changes the appearance of the treated surface. Also, use of nitro-compounds is ecologically undesirable.
Patents of Japan 62-132940; EPW--Japan, 0177364; Japan, 61-221236; Japan; and USSR 1158634 describe pretreatment of materials in a plasma of inorganic gas for 40 sec. to 20 minutes to purify and activate surfaces for subsequent processing. As a result, polymer films deposited by a subsequent polymerization stage adhere better to the treated material surfaces. However, in some instances satisfactory treatment results require discharge power levels which are harmful or destructive to the material being treated.
A prior method of depositing a thin surface film by a plasma polymerization process (Japanese patent 62-132940) includes treatment in a glow discharge of H.sub.2, CO, N.sub.2 or O.sub.2 at p=0.05-5 Torr, t=30 sec--20 min, power 5-50 KWt; then a plasma polymerization stage, followed by plasma treatment in hydrogen. The film obtained by this method is characterized by improved durability, but changes the appearance of the treated surface and physico-mechanical properties of materials.
Japanese patent 61-22136 discloses a method of surface preparation before coating of polyolefine articles which includes the steps of treatment by a fluoro-organic solvent, staining in a glow discharge of oxygen, and coating. The film obtained by this method is characterized by improved strength to peeling and water resistance. Use of fluoro-containing solvent however is an ecologically undesirable feature of this method.
What is needed is a method for imparting liquid resistant surface properties to fabrics and paper products which do not alter the appearance nor physically damage the treated material, which involves a minimum of processing of the item, which can be safely used on various materials, which is not ecologically damaging, and which is simple and dependable.